What this fan controller does on the board
The MAX31785AETL+T is a brushed-DC motor pre-driver with a speed-control function, managed over an I²C bus — it generates the PWM drive signal but leaves the power-stage FETs external, so the thermal load stays off this QFN.
Package reality — 40-TQFN with exposed pad
Housed in a 40-lead TQFN measuring 6x6 mm (the supplier device package is 40-TQFN, 6x6), with an exposed pad underneath for thermal relief — the pad needs a via array to the ground plane to pull heat out of the die when the controller is driving a fan at full duty. Tape & Reel packaging means it feeds into a pick-and-place without a carrier-tape change; the reel quantity is the standard Analog Devices 2.5k or 5k count for QFNs this size. Will it survive the hot air? Yes — the exposed pad is centre-tinned, so preheat the board to 150°C, hit the pad with a 340°C nozzle, and lift the part without lifting the pad.
RoHS3 compliant, which covers the EU RoHS exemption list through the latest recast — no special handling paperwork needed at customs for the European or UK markets. No stock-holding claim — availability verified per request.